A negative-pressure aeration system for composting food wastes

A pilot-scale active aeration reactor was studied for composting food wastes in an open-top container aerated with negative pressure by vacuum. A biological filter bed was used to remove NH3 from the emission. In addition to monitoring system parameters, the compost stability and fertilizer content were also examined to ensure product quality. The compost temperature rose to above 65 °C the first day and maintained at the high temperature fermentation level for 30 days. The pH decreased from the initial 5.2 to 4.3 on the first day and then rose slowly to 7.4 on the 60th day. After 60 days, the C/N ratio dropped from 32 to below 20. The final compost contains 1.6% nitrogen, 0.6% phosphate, and 1.4% potassium with total coliforms below 3 MPN/100 mL. Using the biological filter to remove NH3, the emission contains less than 1 ppm of NH3. This system proves to be effective and environmental friendly.